1. Field of the Invention
The present invention relates to an engine automatic stop and restart apparatus and an engine automatic stop and restart method, which automatically stop an engine when an automatic stop condition is satisfied, and restart the engine when a restart condition is satisfied thereafter.
2. Description of the Related Art
In recent years, there is developed an engine automatic stop and restart apparatus for the purpose of improving fuel consumption of a vehicle such as an automobile and reducing environmental load, in which when a driver's operation satisfies a predetermined condition for stopping an engine (for example, when a pedaling operation of a brake pedal is performed while a vehicle is moving at a speed lower than a predetermined speed), fuel supply is automatically cut off so that the engine is automatically stopped, and after that, when a driver's operation satisfies a predetermined condition for restarting the engine (for example, a releasing operation of the brake pedal, a pedaling operation of an accelerator pedal, and the like), fuel injection is restarted so that the engine is automatically restarted.
As the engine automatic stop and restart apparatus described above, the following apparatus has been conventionally proposed. When an engine rpm becomes equal to or smaller than a predetermined rpm while the engine is rotating by inertia after an operation of automatically stopping the engine is performed, the engine rpm is predicted and calculated in an interval in which the engine rpm is on a decreasing trend. Timing at which a pinion gear is driven is controlled based on meshing-operation time required for a meshing operation of the pinion gear so that the pinion gear comes into meshing engagement with a ring gear when or immediately before the engine rpm becomes zero (for example, see Japanese Patent Application Laid-open No. 2010-276035).
In the above-mentioned conventional apparatus disclosed in Japanese Patent Application Laid-open No. 2010-276035, a state in which the pinion gear and the ring gear are brought into meshing engagement is realized when or immediately before the engine rpm becomes zero. Therefore, the noise generated by meshing engagement can be suppressed.
However, the conventional apparatus has the following problem.
As described above, the conventional apparatus disclosed in Japanese Patent Application Laid-open No. 2010-276035 predicts the engine rpm in the interval in which the engine rpm is on a decreasing trend, which is determined based on the determination that a piston of the engine is at the last top dead center (hereinafter, referred to as “TDC”) after the operation of automatically stopping the engine is performed. In this manner, the control is performed based on the meshing-operation time required for the meshing operation of the pinion gear so that the pinion gear and the ring gear are brought into meshing engagement with each other when or immediately before the engine rpm becomes zero.
For determining the interval in which the engine rpm is on a decreasing trend, whether or not the piston of the engine is at the last TDC is determined. For precisely determining the last TDC, however, the determination is required to be performed by an engine control unit for controlling the engine in view of a load state of the engine, a change of the engine with elapse of time, and the like.
For example, if the load on the engine fluctuates after the determination that the piston of the engine is at the last TDC, and if the degree of decrease in engine rpm becomes smaller and the piston passes through the TDC immediately before the engine is stopped, the engine rpm increases. As a result, at the timing at which the pinion gear comes into meshing engagement with the ring gear, the engine rpm is not zero or not in the vicinity of zero. Therefore, there has been a problem in that the meshing engagement between the pinion gear and the ring gear is not completed until the engine rpm has the trend of decreasing again, resulting in generation of noise.